Fucose and glucosamine addition to alfalfa meal diets improve growth performance, polysaccharide contents, gut microbiota and metabolite profiles of the sea cucumber Apostichopus japonicus

Farming of the sea cucumber Apostichopus japonicus faces challenges due to seaweed overexploitation. Alfalfa meal has proven to be a promising alternative to seaweed meal from the perspective of growth performance of A. japonicus . However, little information is available about the effects of alfalfa meal on other physiological parameters. This study investigated the effect of alfalfa diets and alfalfa diets supplemented with fucose and/or glucosamine on the growth, polysaccharide contents, gut microbiota and metabolite profiles of A. japonicus . Results indicated that growth rate and polysaccharides contents in the body wall of A. japonicus were significantly reduced after seaweed meal was completely replaced by alfalfa meal in the diets. The addition of 1% single monosaccharide (fucose or glucosamine) or compound monosaccharide (fucose and glucosamine) alleviated alfalfa meal-caused growth reduction. Alfalfa meal increased the abundances of the gut bacterial genera Vibrio , Enterococcus , and Shewanella and the richness of gut metabolites, whereas monosaccharide supplementation reduced these changes. Correlation analysis showed that WGR and SGR of A. japonicus were negatively correlated with the contents of melophlin, heptadecanoic, foetidin, and hydroxytridecanoic. Taken together, the addition of fucose and/or glucosamine partially alleviated the reduction in growth performance of A. japonicus caused by the alfalfa diet, possibly by reducing the abundances of the gut harmful genera Vibrio , Enterococcus , and Shewanella .